Two-stroke internal combustion engine with charging cylinder

ABSTRACT

The invention concerns a two-stroke internal-combustion engine with a charging pump, an outlet channel controlled by the main piston being subjected to additional control by the charging-pump plunger. Circulation losses are minimized and a higher means working pressure is obtained by early mechanical closure of the outlet channel by means of the charging-pump plunger or by injecting a pulse of exhaust gases into the outlet channel in the direction opposite to the direction of flow or by injecting part of the intake charge through the outlet channel into the main cylinder. In addition, the formation of oxides of nitrogen is reduced by controlled exhaust gas retention at the combustion stage. The invention also allows a catalytic converter to be used if required, since an increase in the oxygen concentration owing to circulation losses in the outlet channel is avoided.

The invention relates to a two-stroke, reciprocating-piston internalcombustion engine with a charging cylinder arranged parallel with orinclined relative to the main cylinder, in which a single- ordouble-action pump piston is driven by a crankshaft and designed as acylinder slide piston with overflow apertures, and the main cylinder hasan outlet channel controlled by the main piston.

An internal combustion engine is known from U.S. Pat. No. 2,247,147 andNo. 2,417,185, in which the outlet channel is, in the way known per se,exclusively opened and closed by the top edge of the main piston. Forthis reason, the control times for the opening and for the closing ofthe outlet channel are necessarily the same- and the control crosssections are the same as well, even though the control times and thecontrol cross sections should be substantially lower for the closing ofthe outlet channel, so that fewer fresh gases can escape from the maincylinder into the outlet channel when the charge changes. WO 90/0884 A1shows a two-stroke internal combustion engine with crankcase flushing,in which a connection duct is arranged from the crankcase to the outletchannel, through which fresh gas is conveyed and intended to penetratethe cylinder against the exhaust gas flow. Since the control of theconnection duct is dependent on the position of the piston window, theconnection duct is opened in part of the same period of time as theoutlet slot. Therefore, a symmetric control diagram exists. The freshgases thus flow into the outlet channel at an unfavorable point in timebecause the flow of exhaust gas still has a high intensity at such time.By the high vacuum prevailing at the orifice of the connection duct, thefresh gas charge is dragged along from the crankcase and necessarilymixed with the exhaust gas. The flushing pressure of a crankcase-flushedtwo-stroke engine, which pressure is known to be very low, leads to thefact that the flow of fresh gas is not capable of making its way againstthe direction of the flow of exhaust has, which has a larger volume.

It is known that in internal combustion engines with a single outletslot control, as it is used with most two-stroke engines, a relativelylarge proportion of the intake charge escapes through the orifice of theoutlet channel before said orifice is closed by the top edge of thepiston at the end of the change in charge. This impairs the volumetricefficiency and limits the maximally attainable mean operating pressureof such an internal combustion engine to a relatively low level. Afurther drawback, which becomes increasingly more important, is the factthat circulation losses in the exhaust gas falsify the measurement ofthe oxygen content by means of a lambda probe in the exhaust gas duct,and make a catalytic conversion of the nitrogen oxides more difficult.Furthermore, the late closing of the outlet channel also impairs thequality of the mixture formation. So that no parts of the fuel canpenetrate the outlet channel, the fuel or the fuel/air mixture has to beadmitted into the main cylinder relatively late. Therefore, in aninternal combustion engine in which the fuel is directly injected intothe main cylinder, only short times are available for the preparation ofthe mixture until ignition time. In addition, there is the drawback thatthe turbulences of the charging air have subsided as well. This impairsthe formation of the mixture especially at high numbers of revolutionand thus the quality of the combustion. Heretofore, resonance exhaustsystems have been used in order to counteract the occurrence of charginglosses with a retrogressive exhaust gas vibration. This mode ofoperation, however, has little efficiency; it is limited to a verynarrow band of numbers of revolution, and thus inadequate for aninternal combustion engine that is expected to operate economically inall load and rpm-ranges.

The invention is based on the problem of eliminating said deficiencies.Without arranging any additional costly control elements such as valvesor rotary roll slides, the objective is to prevent fresh charge fromescaping from the main cylinder into the outlet channel, and to increaseacross a broad range of numbers of revolution the volumetric degree ofefficiency and thereby the effective mean operating pressure. Thisapplies to internal combustion engines operating according to both theDiesel-process and the Otto-process.

According to the invention, said problem is solved in that at least oneconnection duct, the latter being controlled independently of the mainpiston, is arranged between the charging-pump cylinder and the outletchannel, which duct is controlled by the charging-pump piston, andthrough which part of the charging air precompressed in thecharging-pump cylinder is conveyed into the outlet channel, and throughits orifice against the direction of outflow into the main cylinderwhile the main piston moves upwardly from its lower deadpoint and hasnot yet closed the orifice of the outlet channel. Or in that the spaceof the charging-pump cylinder is divided by separation walls in twochamber; and in that one of said two chambers conveys exhaust gas intothe outlet channel through at least one connection duct, the latterbeing controlled independently of the main piston and being controlledby the charging-pump piston, while the main piston moves upwardly fromits lower deadpoint and has not yet closed the outlet slot of the outletchannel; and in that the direction of inflow of said flow of exhaust gasinto the outlet channel is opposite to the direction of outflow of thecharge losses from the main cylinder. Or in that at least one outletchannel feeding into the charging-pump cylinder is arranged; and in thata duct arranged in the charging-pump piston connects the orifice of theoutlet channel with the orifice of a duct discharging from thecharging-pump cylinder when the main piston opens the outlet slot in themain cylinder; and in that the wall of the charging-pump piston closesthe outlet slot in the charging-pump cylinder earlier than the mainpiston closes the outlet slot in the main cylinder. Useful developmentsof the invention are the subject matter of the dependent claims.

Exemplified embodiments of the subject matter of the invention are shownin the drawings.

FIGS. 1 and 2 snow an exemplified embodiment, in which two connectionducts are arranged between the charging-pump cylinder and the outletchannel.

FIG. 3 shows an exemplified embodiment, in which the outlet channel isdivided by a wall and the connection ducts only feed into the top part.

FIGS. 4 and 5 show an exemplified embodiment, in which the charging-pumpspace is divided in two chambers, of which one conveys, for exampleexhaust gas into the outlet channel.

FIG. 6 shows a channel design as an alternative to the one shown in FIG.5.

FIGS. 7 and 8 show an exemplified embodiment in which an outlet channelleads to the charging-pump cylinder and is additionally controlled bythe charging-pump piston.

FIG. 9 shows a variation of FIG. 7, with an additional overflow aperturein the charging-pump piston.

FIGS. 10 and 11 show another possibility for the channel design.

FIGS. 12 and 13 show a variation in which the charging-pump piston isfitted with a ring channel.

In the internal combustion engine with charging-pump cylinder shown inFIGS. 1 and 2, part of the intake charge is admitted into the maincylinder (1) through the outlet channel (8), whereas the other part isadmitted into the main cylinder (1) in the usual way through directoverflow ducts (11 and 12). In this connection, the individual partquantities and also the time at which intake of such part quantitiesinto the main cylinder (1) starts, are variable within a wide range byarranging the overflow apertures in the charging-pump piston. First,intake charge flows through the overflow ducts (11 and 12) into the maincylinder (1) and expels the residual gases through the outlet channel(8). After the major part of the residual gases has escaped through theoutlet channel (8), the ducts (9 and 10) are released by the recesses(24 and 26) in the charging-pump piston, so that the remaining part ofthe intake charge flows through the outlet channel (8) and into the maincylinder (1). Such flow largely prevents intake charge from escapingfrom the main cylinder (1) and reduces the thermal load on the outletchannel (8).

FIG. 3 shows an exemplified embodiment in which the outlet channel (8)is divided by a wall (13), whereby the connection ducts (9 and 10) onlyfeed into the top part of the outlet channel (8). In this way, theintensity of counterflow is increased, which prevents the intake chargefrom exiting from the main cylinder (1). Since the lower part of theoutlet channel (8) is closed by the main piston (3) much earlier,counterflow is dispensed with in this part of the outlet channel (8).

FIGS. 4 and 5 show an exemplified embodiment in which exiting offlushing gases from the main cylinder (1) is counteracted by a pulsatingexhaust gas counterflow introduced in the outlet channel (8). For thispurpose, the space of the charging-pump cylinder (2) is divided in 2chambers, of which one conveys the intake charge and the other theexhaust gas required for the counterflow. Both chambers (33 and 34) arecontrollable independently of each other by means of butterfly valves.Also, the compression can be different for the two chambers (33 and 34)as required. In this way, it is possible to achieve for each operatingcondition extensive optimization also for controlled exhaust gasretention. With this design, the oxygen content prevailing duringcombustion in the outlet channel (8) can be measured and controlled by alambda probe (14) without falsification. Furthermore, this creates theprecondition for catalytic conversion of the nitrogen oxides. If,through suitable exhaust gas retention, the formation of nitrogen oxidesshould be so low that no catalytic after-treatment is required formeeting the requirements, the chamber (33) also can convey air oranother medium for the counterflow instead of exhaust gas, whereby theair is than available as secondary air for after-oxidizing thehydrocarbons and the carbon monoxide.

FIG. 6 shows an alternative channel design to FIG. 5, whereby theexhaust gas counterflow is introduced by way of a plurality of aperturesalong the circumference of the outlet channel.

FIGS. 7 and 8 show an exemplified embodiment in which the outlet channel(8) leads to the charging-pump cylinder (2), and a duct (20) arranged inthe charging-pump piston (4) connects said piston with the orifice (21)of a duct (22) discharging from the charging-pump cylinder (2) when themain piston (3) opens the outlet channel (18) in the main cylinder (1),so that the exhaust gases flow from the charging-pump cylinder (2)through the duct (22) in this way. Such outflow is stopped by the wall(23) of the charging-pump piston (4) before the main piston (3) closesthe outlet channel (18). Thus only exhaust gases flow through the duct(22) without flushing gases, for which reason the lambda probe (14) isarranged in said duct. It may be advantageous to arranged in the maincylinder (1) additional outlet channels (e.g. 32) which are closed bythe main piston (3) earlier than the outlet channel (18), and which notadditionally controlled by the charging-pump piston (4).

Furthermore, FIGS. 7 and 8 show an advantageous arrangement of the fuelinjection nozzle (15).

FIG. 9 shows an exemplified embodiment in which the outlet channel (18)has at the same time the function of an intake channel. For thispurpose, the wall (23) of the charging-pump piston is provided withanother overflow aperture (35), which is completely open when thecharging-pump piston (4) is in the top dead-point position. This causesprecompressed fresh charge to flow through the outlet channel (18) intothe main cylinder (1). Said flow promotes the preparation of the mixtureespecially when the fuel injection nozzle (15) is arranged oppositely inthe wall of the main cylinder. Another design consists in that a fuelinjection nozzle (15) is arranged in the cylinder head (36), with theinjection jet of said nozzle impacting the wall of the connection duct(20). In this way, superior evaporation of the fuel is achieved, on theone hand, and on the other hand cooling of the wall temperature. Due tothe division of the charging-pump cylinder (2) in 2 chambers, one of thelatter can convey air via the overflow channels (11 and 12) and theother a fuel-air mixture--which is precompressed in said otherchamber--through the overflow aperture (35) in the charging-pump piston(4), into the main cylinder (1)

FIGS. 10 and 11 show an exemplified embodiment with a channel layoutdifferent from the one in FIGS. 7 and 8, whereby an outlet channel (18)additionally controlled by the charging-pump piston (4) feeds into anoutlet channel (32) exclusively controlled by the main piston (3). Inthis embodiment, too, the outlet channel (18) can be used--as alreadydescribed above and shown in FIG. 9--for the inflow of the fresh chargeinto the main cylinder (1)

FIGS. 12 and 13 show an exemplified embodiment in which thecharging-pump piston (4) is provided with an outwardly open ringchannel, through which the exhaust gases flow to the duct (22)discharging from the charging-pump cylinder. The control edge (38) ofthe charging-pump piston (4) closes in this connection the bottom edgeof the orifice (20) of the outlet channel (22) earlier than the mainpiston (3) closes the orifice (17) of the outlet channel (18) in themain cylinder (1).

Furthermore, in the figures, the reference numeral 5 denotes the pistonrod and reference numeral 6 the crankshaft.

I claim:
 1. Two-stroke, reciprocating-piston internal combustion engine with a charging-pump cylinder arranged parallel with or inclined relative to the main cylinder, in which the pump piston and the main piston are connected in terms of drive by a crankshaft, the pump piston is designed as a cylinder slide piston with overflow apertures, and the main cylinder has a piston-controlled outlet channel, characterized in that at least one connection duct (9), the latter being controlled independently of the main piston (3), is arranged between the charging-pump cylinder (2) and the outlet channel (8), said connection duct being controlled by the charging-pump piston (4) and conveying part of the charging air precompressed in the charging-pump cylinder (2) into the outlet channel (8) and through an outlet slot (16) against the outflow direction into the main cylinder (1), while the main piston (3) moves from its lower deadpoint upwardly and has not yet closed the outlet slot (16) of the outlet channel (8).
 2. Internal combustion engine according to claim 1, characterized in that the overflow apertures (26 and 27) in the wall (23) of the charging-pump piston (4) open overflow ducts (11 and 12) earlier than overflow apertures (24 and 25) open the at least one connection duct (9 and 10).
 3. Internal combustion engine according to claim 1, characterized in that the length of the at least one connection duct (9 and 10) is greater than the length of an overflow duct (11 and 12).
 4. Internal combustion engine according to claim 1, characterized in that the height of the outlet channel (8) is divided by a wall (13), and that the at least one connection duct (9 and 10) only feed into the upper part of the outlet channel.
 5. Internal combustion engine according to claim 1, characterized in that one or several outlet channel(s) (e.g. 32) is/are additionally arranged in the main cylinder (1), said channel(s) being closed by the main piston (3) in the main cylinder (1) earlier than the outlet channels (8 and 18), respectively.
 6. Two-stroke, reciprocating-piston internal combustion engine with a charging-pump cylinder arranged parallel with or inclined relative to the main cylinder, in which the pump piston and the main piston are connected in terms of drive by a crankshaft and the pump piston is designed as a cylinder slide piston with overflow apertures, and the main cylinder has a piston-controlled outlet channel, characterized in that the space of the charging-pump cylinder (2) is divided by separation walls (29, 30) in two chambers; that through one of said two chambers (33, 34), exhaust gas is conveyed through at least one connection duct (31), the latter being controlled independently of the main piston and controlled by the charging-pump piston (4), into the outlet channel (8) while the main piston (3) moves from its lower deadpoint upwardly and has not yet closed an outlet slot (16) of the outlet channel (8); that the inflow direction of said flow of exhaust gas into the outlet channel (8) is opposite to the outflow direction of parts of the charge from the main cylinder (1); and that through the second chamber, charging air or a fuel/air mixture is conveyed through overflow ducts (11, 12) into the main cylinder (1).
 7. Internal combustion engine according to claim 6, characterized in that precompression of the two chambers (33 and 34) can be different.
 8. Internal combustion engine according to claim 6, characterized in that the division of the charging-pump space in two chambers by the separation walls (29 and 30) takes place before the overflow apertures (26 and 27) of the charging-pump piston (4) open the overflow ducts (11 and 12), and that only one short inlet pipe (28) with a valve (6) is arranged.
 9. Two-stroke, reciprocating-piston internal combustion engine with a charging-pump cylinder arranged parallel with or inclined relative to the main cylinder, in which the pump piston and the main piston are connected in terms of drive by a crankshaft and the pump piston is designed as a cylinder slide piston with overflow apertures and the main cylinder has a piston-controlled outlet channel, characterized in that at least one outlet channel (18) feeding into the charging-pump cylinder (2) is arranged; that a duct (20) arranged in the charging-pump piston (4) connects an orifice (19) of the outlet channel (18) with an orifice (21) of a duct (22) discharging from the charging-pump cylinder (2) when the main piston (3) opens an outlet slot (17) of the outlet channel (18) in the main cylinder (1); that the wall (23) of the charging-pump piston (4) closes the orifice (19) of the outlet channel (18) in the charging-pump cylinder (2) earlier than the main piston (3) closes the outlet slot (17) of the outlet channel (18); and that the charging air or the fuel/air mixture is conveyed through the overflow ducts (11, 12) into the main cylinder.
 10. Internal combustion engine according to claim 9, characterized in that at least one overflow aperture (35) is arranged in the wall (23) of the charging-pump piston (4), said overflow aperture connecting the space of the charging-pump cylinder (2) with the outlet channel (18) as soon as the connection of the outlet channel (18) with the duct (22) is interrupted, so that fresh gas flow from the charging-pump cylinder (2) through the outlet channel (18) into the main cylinder (1).
 11. Internal combustion engine according to claim 9, characterized in that a fuel injection nozzle (15) is arranged in the wall of the main cylinder (1), the injection jet of said nozzle being directed at the outlet slot (17) of the outlet channel (18).
 12. Internal combustion engine according to claim 9, characterized in that an injection nozzle is arranged in the cylinder head (86) of the charging cylinder, the fuel jet of said nozzle being directed at the wall of the duct (20) of the charging-pump piston (4). 